Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
  • B29C49/42—Component parts, details or accessories; Auxiliary operations
  • B29C49/58—Blowing means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
  • B29C49/42—Component parts, details or accessories; Auxiliary operations
  • B29C49/78—Measuring, controlling or regulating
  • B29C49/783—Measuring, controlling or regulating blowing pressure
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
  • B29C49/42—Component parts, details or accessories; Auxiliary operations
  • B29C49/78—Measuring, controlling or regulating
  • B29C49/783—Measuring, controlling or regulating blowing pressure
  • B29C2049/7831—Measuring, controlling or regulating blowing pressure characterised by pressure values or ranges
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
  • B29C49/42—Component parts, details or accessories; Auxiliary operations
  • B29C49/78—Measuring, controlling or regulating
  • B29C2049/788—Controller type or interface
  • B29C2049/78805—Computer or PLC control
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C2949/00—Indexing scheme relating to blow-moulding
  • B29C2949/07—Preforms or parisons characterised by their configuration
  • B29C2949/0715—Preforms or parisons characterised by their configuration the preform having one end closed
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
  • B29C49/02—Combined blow-moulding and manufacture of the preform or the parison
  • B29C49/06—Injection blow-moulding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
  • B29C49/08—Biaxial stretching during blow-moulding
  • B29C49/16—Biaxial stretching during blow-moulding using pressure difference for pre-stretching, e.g. pre-blowing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
  • B29C49/42—Component parts, details or accessories; Auxiliary operations
  • B29C49/4289—Valve constructions or configurations, e.g. arranged to reduce blowing fluid consumption
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
  • B29C49/42—Component parts, details or accessories; Auxiliary operations
  • B29C49/78—Measuring, controlling or regulating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2031/00—Other particular articles
  • B29L2031/712—Containers; Packaging elements or accessories, Packages
  • B29L2031/7158—Bottles

Definitions

• the invention relates to the manufacture of containers by blow molding or stretch blow molding, from plastic blanks.
• a container To manufacture a container according to the blowing technique, it is first heated by a blank (whether a preform or an intermediate container having undergone a first blowing operation from a preform) to a temperature greater than the glass transition temperature of the constituent material of the blank.
• the blank is then introduced into a mold, and then the blank is blown by injecting a gas (such as air) under high pressure (generally greater than 30 bars).
• a gas such as air
• high pressure generally greater than 30 bars.
• the stretch-blow technique consists in stretching the blank with a sliding rod, in particular to minimize the misalignment of the container and to make the distribution of the material as uniform as possible.
• a pre-blowing operation during which the gas is injected into the blank under a reduced pressure (generally between 5 ° C.). and 16 bars). It is during the pre-blowing operation that drawing of the blank is carried out, blowing only afterwards.
• the duration of the process of manufacturing a container, between the instant of introduction of the blank into the mold and the moment of ejection of the formed container is a few seconds.
• the duration of pre-blowing it is only a few tenths of a second.
• the invention aims in particular to remedy these disadvantages, by proposing a method for improving the quality of the containers produced, while limiting the scrap, and maintaining - or increasing - production rates.
• the invention proposes, according to a first object, a method for manufacturing a container by stretching in a mold from a plastic blank, which comprises the steps of: heating the blank to a predetermined heating temperature; introduce the blank into the mold; stretching the blank by means of a rod moved at a predetermined drawing speed; at a predetermined time, referred to as a pre-blast, controlling the opening of a solenoid valve to communicate the interior of the blank with a gas source at a pre-blowing pressure and a pre-blast flow rate predetermined; measure the pressure inside the blank; detect a peak pressure; memorizing the moment at which this pressure peak occurs as well as the corresponding pressure prevailing in the blank; comparing the instant and the pressure of the detected peak with, respectively, a predetermined instant and pressure of a theoretical pressure peak; if the measured peak and the theoretical peak are not confounded, modify at least one of the following parameters: pre-blowing pressure, pre-blowing flow, pre-blowing top, stretching speed, heating temperature.
• the following adjustment operations can be performed, depending on the situations observed: if the instant and the pressure of the detected peak are respectively before and below the instant and at the pressure of the theoretical peak, lowering the heating temperature. if the instant and the pressure of the detected peak are, respectively, anterior and equal to the instant and the pressure of the theoretical peak, reduce the pre-blowing pressure or flow.
• An additional operation may in this case be to reduce the heating temperature. if the instant and the pressure of the detected peak are, respectively, anterior and greater than the instant and the pressure of the theoretical peak, reduce the pre-blowing pressure or flow rate. if the instant and the pressure of the detected peak are, respectively, equal to and greater than the instant and the pressure of the theoretical peak, reduce the pre-blowing pressure or flow rate.
• an additional operation may be to increase the heating temperature. if the moment and the pressure of the detected peak are, respectively, posterior and greater than the instant and the pressure of the theoretical peak, increasing the heating temperature. In this case, an additional operation may consist in reducing the pre-blowing flow rate and / or advancing the pre-blast top. if the moment and the pressure of the detected peak are, respectively, posterior and equal to the instant and the pressure of the theoretical peak, increase the pre-blowing pressure or flow rate. In that case, an additional operation may be to increase the heating temperature. if the instant and the pressure of the detected peak are, respectively, posterior and inferior to the instant and the pressure of the theoretical peak, increasing the pressure or the pre-blowing flow rate. if the instant and the pressure of the detected peak are, respectively, equal to and less than the time and pressure of the theoretical peak, increasing the pre-blowing pressure or flow rate. In this case, an additional operation may consist of reducing the heating temperature.
• the invention further provides a method of making a container by stretch blow molding in a mold from a plastic blank, which comprises the steps of: heating the blank to a predetermined heating temperature; introduce the blank into the mold; stretching the blank by means of a rod moved at a predetermined drawing speed; at a predetermined time, referred to as a pre-blast, controlling the opening of a solenoid valve to communicate the interior of the blank with a gas source at a pre-blowing pressure and a pre-blast flow rate predetermined; measure the pressure inside the blank; detect a peak pressure; memorize the moment at which this peak of pressure occurs; comparing the instant of the detected peak with a predetermined instant of a theoretical pressure peak; if the measured instant and the theoretical moment are not confounded, modify at least one of the following parameters: pre-blowing pressure (P P ), pre-blowing flow, pre-blowing top, drawing speed, heating temperature.
• P P pre-blowing pressure
• the invention further provides a method of making a container by stretch blow molding in a mold from a plastic blank, which comprises the steps of: heating the blank to a predetermined heating temperature; introduce the blank into the mold; stretching the blank by means of a rod moved at a predetermined drawing speed; at a predetermined time, referred to as a pre-blast, controlling the opening of a solenoid valve to communicate the interior of the blank with a gas source at a pre-blowing pressure and a pre-blast flow rate predetermined; measure the pressure inside the blank; detect a peak pressure; memorizing the pressure prevailing in the blank corresponding to the peak pressure; comparing the pressure of the detected peak with a predetermined pressure of a theoretical pressure peak; if the measured pressure and the theoretical pressure are not confounded, modify at least one of the following parameters: pre-blowing pressure, pre-blowing flow, pre-blowing top, stretching speed, heating temperature.
• a further object of the invention is a machine for manufacturing containers from plastic blanks, which comprises: an oven provided with means for heating the blanks; a mold having a cavity for receiving a blank; a source of gas at a predetermined pre-blowing pressure; a solenoid valve adapted to put in communication the inside of the blank, received in the cavity, with said gas source, at a predetermined pre-blowing rate; means for controlling the opening of the solenoid valve at a predetermined time called pre-blast top; a sensor capable of measuring the pressure prevailing in the blank; means for detecting an instant, said instant of development, in which a peak of pressure occurs in the blank; means for comparing the instant of development and the so-called development pressure, prevailing in the preform at this time, with, respectively, a time and a theoretical pressure of development; means for regulating the pre-blowing rate as a function of this comparison.
• this machine further comprises: means for regulating the pre-blowing pressure as a function of the comparison between the instant and the development pressure with the theoretical instant and pressure of development; means for regulating the heating temperature as a function of the comparison between the instant and the development pressure with the theoretical instant and pressure of development. means for regulating the pre-blast top as a function of the comparison between the instant and the development pressure with the theoretical instant and pressure of development.
• the machine preferably comprises: an elongation rod displaceable at a predetermined drawing speed; means for regulating the drawing speed as a function of the comparison between the instant and the development pressure with the time and the theoretical development pressure.
• a further object of the invention is a computer program product intended to be implemented on a container manufacturing machine as described above, which includes instructions for: controlling the opening of the solenoid valve; take into account the moment of development; take into account the development pressure; take into account the theoretical moment of development; take into account the theoretical pressure of development; compare the moment of development with the theoretical moment of development; compare the development pressure with the theoretical development pressure; regulating at least one of the following parameters: pre-blowing pressure, pre-blowing flow, pre-blowing top, drawing speed, heating temperature according to the result of these comparisons.
• FIG. 1 is a schematic view showing a container manufacturing machine
• Figure 2 is a schematic sectional view partially showing a molding unit within the machine of Figure 1
• FIG. 3 is a diagram on which is drawn a curve illustrating the variations of the pressure prevailing in a blank during the manufacture of a container
• FIG. 4 is a diagram on which a curve is plotted illustrating the variations of the pressure prevailing in the blank during the pre-blowing operation
• Figs. 5A to 5H are sectional views showing the blank in the mold at various stages during pre-blowing;
• FIG. 1 is a schematic view showing a container manufacturing machine
• Figure 2 is a schematic sectional view partially showing a molding unit within the machine of Figure 1
• FIG. 3 is a diagram on which is drawn a curve illustrating the variations of the pressure prevailing in a blank during the manufacture of a container
• FIG. 4 is a diagram on which a curve is plotted illustrating the variations of the pressure prevailing in the blank during the pre-blowing operation
• FIG. 6 is a diagram showing the superposition of two pressure curves respectively corresponding to two different instants of opening control of a pre-blowing solenoid valve
• FIG. 7 is a diagram showing the superposition of two pressure curves respectively corresponding to two distinct values of the pre-blowing pressure or flow rate
• FIG. 8 is a diagram showing the superposition of two pressure curves respectively corresponding to two distinct values of the stretching speed
• Figure 9 is a diagram showing the superposition of two pressure curves respectively corresponding to two distinct values of the heating temperature of the blank
• FIG. 10 is a diagram showing the superposition of two pressure curves respectively corresponding to two instants of opening control of a blowing solenoid valve.
• Figure 1 a machine 1 for the manufacture of containers 2 from blanks 3 of plastic such as PET (polyethylene terephthalate).
• the blanks 3 are preforms from which the final containers 2 are directly obtained without passing through an intermediate container.
• Each preform 3 comprises a neck 4 (which does not undergo deformation during the formation of the container 2), and a cylindrical body 5 terminated by a hemispherical bottom 6.
• This machine 1 comprises a tunnel type furnace 7, in which the preforms 3 are heated on the runway at a temperature greater than the glass transition temperature of their constituent material.
• the heating temperature is preferably between 100 ° C. and 140 ° C.
• the machine 1 further comprises a plurality of molding units 8 mounted on a rotating carousel 9 disposed at the outlet of the furnace 7 with the interposition of a transfer wheel 10 ensuring the synchronization of the heating and molding operations of the preforms 3.
• Each molding unit 8 comprises a mold 11, made of steel or aluminum alloy, comprising two half-molds 12, 13 and a mold base 14 which together define an internal cavity 15 intended to receive a preform 3 coming from 7.
• Each molding unit 8 further comprises: a rod 16 of elongation slidably mounted relative to the mold 11 along a main axis X (generally of revolution) thereof, between a high position (FIG. 2) allowing the introduction of the preform 3 and a low position ( Figure 5H) where, at the end of the stretching of the preform 3, the rod 16 reaches the mold base 14 by pressing the bottom 6 thereof.
• a housing 17 defining a nozzle 18 in which slides the rod 16 and which, during the manufacture of the container 2, cooperates with the neck 4 of the preform 3.
• the molding unit 8 furthermore comprises a plurality of fluidic circuits opening into the nozzle 18 via the casing 17, namely: a circuit 19 for pre-blowing air at medium pressure (between 5 and 16 bars), this circuit 19 comprising a source of pre-blowing air and a duct 21 (which may be formed at least partially in the casing 17) connecting this source 20 to the nozzle 18 with the interposition of a first solenoid valve 22, said pre-blowing solenoid valve, a circuit 23 of high pressure blowing air (between 30 and 40 bars), comprising a source 24 of blowing air and a duct 25 (which may be formed at least partially in the housing 17) connecting this source 24 to the nozzle 18 with the interposition of a second solenoid valve 26, called the blow-off solenoid valve, a degassing circuit 27 comprising a vent 28 and a conduit 29 connecting the nozzle 18 to the mouth 28 with the interposition of a third solenoid valve 30, said degassing solenoid valve.
• the solenoid valves 22, 26, 30 are electrically connected to a control unit 31 which controls its opening and closing (taking due account of their response times). These solenoid valves may 22, 26, 30 be spaced apart from the housing; however, for greater compactness, they are preferably at least partially included in it, in accordance with the embodiment described in the French patent application published under the number FR 2 872 082 or in the international equivalent application published under the number WO 2006/008380, both documents in the name of the applicant and which the skilled person can refer.
• the molding unit 8 is further provided with a pressure sensor 32 by which the pressure in the preform 3 is measured during the manufacture of the container 2.
• the sensor 32 connected to the unit 31 control which stores the pressure measurements made, is provided with a sensitive portion 33 opening into the nozzle 18 (where the pressure is identical to that prevailing in the preform 3).
• the manufacture of a container 2 from a preform 3 is performed as follows.
• the preform 3, mounted on a conveyor, is first introduced into the furnace 7 where it is heated, neck 4 downwards, under the conditions described above.
• the preform 3 is gripped by a clamp of the transfer wheel 10 and introduced, after being turned to be oriented neck 4 at the top, in a mold 11 previously opened.
• the elongation rod 16 is in the up position.
• the mold 11 closes on the preform 3.
• the top start t D constitutes the origin of the time axis (abscissa) in FIGS. 3, 4 and 6 to 10. From this instant on, the pressure P prevailing in the preform is continuously measured, each value being stored in memory. in the control unit 31.
• the term "continuous" means that the period at which the pressure measurements are made is small in comparison with the time required for the pressure variations in the preform 3.
• a high performance sensor 32 will be chosen, making it possible to carry out measurements. pressure measurements at a period of less than or equal to 5 ms (millisecond), preferably less than or equal to 2 ms, the ideal being to be able to perform the measurements at a period of 1 ms.
• start t D corresponds to a predefined angular position of the mold 11 on the circumference of the carousel 9.
• the control of the displacement of the elongation rod 16 is purely mechanical, performed by means of a cam against which rolls or slides a cam follower integral with the rod 16 of elongation.
• the moment when the rod 16 of elongation begins its descent is coincident with the start t D , which corresponds to the moment when the cam follower comes into contact with the cam.
• the displacement of the rod 16 of elongation is provided by an electromechanical system controlled by the control unit 31.
• the moment when the descent of the elongation rod 16 begins is shifted with respect to the starting point t D by an offset value equal to the response time of the electromechanical system.
• This offset value provided by the manufacturer of the system, is taken into account in the setting of the top start to so that the descent of the rod 16 of elongation begins as soon as possible after the closure of the mold 11.
• V E the speed of displacement of the rod 16 of elongation, this speed also being referred to as drawing speed.
• the control unit 31 controls the opening of the pre-blast solenoid valve 22. for communicating the interior of the preform 3 with the source of pre-blowing air.
• the instant referred to as the actual pre-blast start time and noted t A , from which the pressure P in the preform 3 begins to increase, lags behind the pre-blast top t P , equal to the response time of the solenoid valve 22 pre-blowing.
• This delay is taken into account in the setting of the pre-blast top t P , so that the real time t A start of pre-blowing starts after the moment when the rod
• the elongation reaches the bottom of the preform 3, which instant can be calculated in a simple manner from the (known) descent speed of the elongation rod 16 and the length (also known) of the preform 3.
• From point A begins an axial expansion phase of the preform 3.
• the slope of the pressure curve at point A is zero on the left, and positive on the right.
• the pressure in the preform 3 increases as it is stretched, the air flow introduced into the preform 3 being greater than the increase in the internal volume of the preform 3 (which does not undergo any expansion radial, see Figure 5C), until a moment, referred to as development time and noted t B , where the plastic flow threshold of the preform 3 has been reached.
• t B occurs a peak pressure, the corresponding point, called development point, being noted B in Figures 4 and 7 to 9.
• the slope of the blowing curve is zero, this slope s' inverting from left (where it is positive) to right (where it is negative) from point B.
• the corresponding pressure, called development pressure, is noted P 8 .
• This radial expansion phase ends at a time, referred to as end time expansion, denoted thee, where the preform 3 has reached the surface of the cavity 15 over substantially the entire its height, in other words when the internal volume of the preform 3 is almost equal to the final volume of the container 2, with the exception of localized areas where the contact between the preform 3 and the cavity 15 is not complete for example in areas where are formed ribs, grooves or other recesses to give the container 2 a better hold or a certain aesthetics (Figure 5H).
• end time expansion denoted thee
• the start time D of the start of blowing shows a slight delay with respect to a moment, referred to as "blow-out” and noted t s , at which the control unit 31 simultaneously controls the closing of the pre-blowing solenoid valve 22 and the opening of the blowing solenoid valve 26.
• t D of the start of blowing corresponds on the pressure curve a singular point, called blow start point and denoted D, where the curve bends and shows a significant increase in its slope.
• pre-blowing is a determining factor in the quality of the final container.
• the pre-blowing control is carried out by means of the drawing of the corresponding pressure curve.
• all containers are identical.
• the repeatability of the manufacturing process is not ensured due to the variations of physical parameters (pressure, temperature) and mechanical (solenoid response time, clogging of pneumatic circuits, leaks in the pre-blowing circuits and blowing, etc.) which can affect the different molding units 8 of the machine 1 during production of the containers 2. This is why there are significant differences between the containers 2.
• the inventors propose to ensure a continuous regulation of pre-blowing operations by feedback on at least one of the following parameters: i. heating temperature T of the preforms; i. pressure P P of pre-blowing; iii. flow rate D P of pre-blowing; iv. drawing speed V E ; v. prepuffing t P ; vi. top blowing t s .
• the inventors have considered that it is illusory to try to obtain for each container produced a curve strictly identical to the theoretical pre-blowing curve and therefore propose a simpler control method while being effective.
• at least one characteristic point defined by a doublet time / pressure, judged characteristic of the smooth running of the pre-blowing operations, is selected on the theoretical curve, and a zone of tolerance is defined around this point, a combination of a tolerance of time (along the abscissa axis) and a pressure tolerance (along the y-axis), in particular to take into account the error margins on the measurements made.
• the real point is compared with the corresponding theoretical characteristic point.
• the real and theoretical points are decreed together.
• the real and theoretical points are decreed distinct, in which case, as we shall see below, feedback measures can be taken to modify at least the one of the parameters listed above in order to converge, on the pressure curve of the next container, the real point towards the theoretical point.
• the real A point is compared with the theoretical A point. Insofar as the pressure at the point A is zero, in practice we compare the instant t A of the real point A with the instant of the theoretical point A, that is to say the theoretical start time of pre-blowing. to check if the time t A of the real point A is within the tolerances defined for point A.
• the pre-blowing top t P is delayed.
• the two curves plotted in solid lines in FIG. 6 illustrate two different settings of the pre-blowing top t P.
• the curve on the left illustrates an advance of the pre-blast top t P ; on the contrary, the curve on the right illustrates a delay of the pre-blowing top t P.
• the theoretical curve is, between them, drawn in dashed lines.
• the machine 1 comprises: means for detecting the real time t A of the beginning of pre-blowing; means for comparing this instant t A with the theoretical start time of pre-blowing; and means for regulating the pre-blowing top t P according to the result of this comparison.
• the machine 1 also comprises means for storing a plurality of points A (for example a dozen) detected on a series of containers 2 manufactured, in particular for statistical study purposes.
• Point B may be in the form of instructions of a computer program product implemented in the control unit 31 of the machine 1.
• Regulating the development instant t B (abscissa of the point B) makes it possible to control the radial expansion of the preform 3.
• An early occurrence, or, on the contrary, a late occurrence of the development point B can similarly testify to a bad distribution of the material, resulting in a defect in the holding of the container 2.
• this measurement can be carried out either during manufacture of the container 2, or preferably a posteriori, directly on the pre-blowing curve.
• the real point B is then compared with the theoretical point B.
• the real development time t B with the theoretical development time and, on the other hand, the actual development pressure P 8 with the theoretical development pressure to verify both. are within the tolerances defined for B.
• the real point B is decreed coincident with the theoretical point B when it is in the tolerance zone defined around the theoretical point B.
• the modification of the pre-blowing top t P produces a shift of point A, to the right on the time axis when the pre-blowing top t P is delayed, or on the contrary to the left when the pre-blowing top t P is advanced .
• this modification affects the whole of the pre-blowing curve, which is offset in the same direction as the point A.
• the modification of the pre-blowing top t P thus affects the development instant t B , ie say the abscissa of point B. Assuming that the actual time t B of development is either before or after the theoretical moment of development, a simple measure could be to delay or respectively advance the top pre-blowing t P.
• FIG. 7 illustrates the influence of the pressure P P or the flow rate P P of pre-blowing on the progress of pre-blowing. It has been found that the influence of the pressure P P is similar to that of the flow rate D P. The common influence of these two parameters can therefore be reduced to the influence of their product P P ⁇ D P : the increase of this product can result from an increase of the pre-blowing pressure P P with a constant flow rate Dp an increase in the prepump rate D P at constant pressure Pp, or a simultaneous increase of both D P and P P ; on the contrary, a decrease in the product P P ⁇ D P may result from a decrease in the prepuffing pressure P P at a constant flow rate D P , a decrease in the prepuffing flow rate D P at a constant pressure P P , or a simultaneous decrease in pressure D P and flow D P , it being understood that increasing one while decreasing the other does not appear useful.
• the curve on the left corresponds to a product value P P ⁇ D P greater than that corresponding to the curve on the right: it can be seen that an increase in the product P P ⁇ D P results in an increase in the slope of the pressure curve at point A (that is to say at the real time t A of the beginning of pre-blowing), an anticipation of the instant of development t B and an increase in the development pressure P B (on the curve, the point B is thus displaced upwards and to the left).
• a decrease in the product P P ⁇ D P causes a decrease in the slope of the pressure curve at point A, a delay in the development instant t B and a decrease in the development pressure P B (on the curve , point B is moved down and to the right).
• FIG. 8 illustrates the influence of the drawing speed V E on the pre-blowing progress.
• a drawing speed V E greater than that corresponding to the upper curve.
• Figure 9 illustrates the influence of the heating temperature T on the course of pre-blowing.
• a heating temperature T greater than that corresponding to the upper curve. It can be seen that the increase in the heating temperature T has an influence similar to the increase in the stretching speed V E : anticipation of the development instant T B and reduction of the development pressure P B , whereas decreasing the heating temperature T has a similar effect to the reduction in speed V E drawing: delay time t B of development and increasing the pressure P B development.
• the pre-blowing top t P is, in practice, modified only when modifications of the pressure Pp, of the flow rate D P or the heating temperature T were not sufficient to bring the development point B back to its tolerance zone.
• the stretching speed V E it is only modified to refine the positioning of the development point B (and provided that the machine 1 is provided with means for adjusting the drawing speed V E ).
• the displacement of the development point B (especially its abscissa, the development time t B ) has an effect on the time t c of the end of expansion (abscissa of the point C).
• Parameter changes affecting the position of the point B may therefore lead to having to modify the position of the point D (that is to say, depending on the case, to advance or delay the top blow t s ) which can indeed be found offset from point C; the corresponding settings are shown below.
• the machine 1 comprises: means for detecting the development instant t B ; means for comparing the development time t B and the development pressure P B with, respectively, the theoretical development time and pressure; means for regulating the prepuffing flow Dp as a function of this comparison.
• These means may be in the form of instructions of a computer program product implemented in the control unit 31 of the machine 1.
• the machine 1 comprises, for example, a regulator 34 flow rate mounted on the pre-blowing solenoid valve and controlled by the control unit 31 (see Figure 2).
• the machine 1 may, depending on the parameters that one chooses to regulate, include, for example in the form of additional instructions of the computer program: means for regulating the pressure P P of pre-blowing as a function of the comparison between real point B and theoretical point B; means for regulating the heating temperature T as a function of the comparison between the real point B and the theoretical point B; means for regulating the pre-blast top t P as a function of the comparison between the real point B and the theoretical point B; means for regulating the stretching speed V E as a function of the comparison between the real point B and the theoretical point B.
• the peak pressure is detected and one acts on at least one of the following parameters: prepuffing pressure P P , prepuffing flow rate D P , prespeeding top t P , drawing speed V E , temperature T to advance or, on the contrary, delay the development time t B.
• the pressure peak is detected and one acts on at least one of the following parameters: prepuffing pressure P P , prepuffing flow rate D P , prespelling top t P , drawdown speed V E , temperature T heating to increase or, conversely, decrease the development pressure P B.
• the machine 1 also comprises means for storing a plurality of points B (for example a dozen) detected on a series of containers 2 manufactured, in particular for statistical study purposes.
• Points C. D Recall that the point C corresponds to the end of the expansion of the preform 3, when it has reached the surface of the cavity 15 over substantially its entire height, that is to say when the internal volume of the preform 3 has almost reached the final volume of container 2. At point C, the pressure curve bends and shows an increase in its slope.
• the occurrence of the point C is thus detected, that is to say the instant t c from which the pressure in the preform 3 begins to increase in a linear fashion (instant of end of expansion). Then, in the event that the top blowing t P is later than the instant of end of expansion, we advance the top blowing to converge the point D to the point C.
• the time interval separating the instant end of expansion of the top blowing t s is measured, and the top blowing t s is advanced by a value equal to this delay.
• the response time of the blow-off solenoid valve 26 must be taken into account, because of which the actual time T D of the start of blow (abscissa of the point D) is slightly posterior to the blow-off time t s .
• the points C and D are assumed to be merged when the delay separating the end time t c of expansion of the instant t D of the start of blowing (or the time separating the instant t c of end of expansion of the blowing t s increased of the response time of the solenoid valve 26 blowing) is less than one predetermined value.
• FIG. 10 shows two curves: the right one corresponds to the presence of a gap between the end of expansion time t c and the start time t D of the start of blowing.
• the left curve in dashed lines, corresponds to a regulation carried out by feedback on the basis of the curve of right: one advanced the top blowing t s of the value of the difference separating on the curve of right the moment t c from the moment t D.
• the machine 1 comprises: means for detecting the instant t c of end of expansion; and means for regulating the blowing ts according to the instant tc of end of expansion. More specifically, the machine 1 may comprise: means for detecting the moment t D of the start of blowing; and means for comparing the instant t c to end of expansion with time t D of the beginning of blowing, the regulating means being provided for moving the top blow t s of the value of the gap between them.
• the machine 1 also comprises means for storing a plurality of points C and / or D (for example a dozen) detected on a series of containers 2 manufactured, in particular for statistical study purposes.
• the machine 1 may comprise means for comparing the instant of end of expansion with the pre-blast top ts, the regulation means being provided to advance the blowing ts of the value of the distance between them, increased the response time of the blow-off solenoid valve 26.
• These means may be in the form of instructions of a computer program product implemented in the control unit 31.

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• Engineering & Computer Science (AREA)
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• Mechanical Engineering (AREA)
• Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)

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• 2006
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• 2007
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  • 2007-12-04 JP JP2009539780A patent/JP5235895B2/ja active Active
  • 2007-12-04 MX MX2009005955A patent/MX2009005955A/es active IP Right Grant
  • 2007-12-04 CN CN200780045101.9A patent/CN101547783B/zh active Active
  • 2007-12-04 EP EP07870378.2A patent/EP2101984B1/de active Active
  • 2007-12-04 WO PCT/FR2007/001991 patent/WO2008081108A2/fr active Application Filing

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